Novel alpha-Bi2O3 nanosheets have been successfully synthesized by graphite oxide (GO)-assisted sono-chemical route and subsequent calcining treatment. The morphology of the final products can be controlled by tuning GO nanosheets in the synthesis process. Porous and nanosheet-covered alpha-Bi2O3 microrods have also been obtained, and the growth mechanism has been discussed. Scanning electron microscopy and transmission electron microscopy analyses reveal that the alpha-Bi2O3 nanosheets are 10-20 nm in thickness with suppressed growth along the [2 1-4] direction. Owing to the unique structure, the alpha-Bi2O3 nanosheets show broader optical absorption and narrower band gap (2.25 eV) as compared to other two forms of alpha-Bi2O3 (similar to 2.8 eV). Photocatalytic experiments demonstrated that the alpha-Bi2O3 nanosheets exhibited excellent activity much higher than the porous and nanosheet-covered alpha-Bi2O3 microrods in degrading organic pollutants under visible light. This study opens up a new route for the preparation of alpha-Bi2O3 nanosheets with superior photocatalytic performance.